Project Summary Many bacteria form complex multicellular communities known as biofilms. Biofilms are a common source of human infections and are specifically associated with chronic infections and with infections resulting from biomedical implants. Biofilm-derived infections are particularly difficult to treat since the structure of biofilms provides bacteria with resistance to diverse environmental stresses, antimicrobial agents, and host immune systems. In contrast to the negative impact of biofilms from some bacteria on human health, biofilms from other bacteria have productive roles in ecology and agricultural settings. Despite the importance and ubiquity of biofilms, most microbial investigations focus on cultures of free-living bacterial cells. Thus, the precise mechanisms that signal biofilm assembly remain largely unknown. In contrast to the impact of biofilms on human health, little is understood about how bacteria interpret and respond to environmental cues to form a biofilm. This project will use the bacterial model organism Bacillus subtilis to characterize the molecular basis of biofilm formation. In its natural environment, B. subtilis colonizes and forms biofilms on the roots of some crops resulting in a positive growth effect on the plant. How do plants and B. subtilis communicate to promote biofilm formation? This project focuses on three types of proteins that have the potential to recognize chemical signals from plants and elsewhere in the B. subtilis environment. By identifying the chemicals these proteins bind, as well as how the proteins interact with each other, this project will help elucidate how biofilm assembly is initiated. The experiments in this research project will provide fundamental knowledge about the nature of how bacteria respond to their environments, as well as how they form bacterial communities in natural settings. This knowledge has the potential to lead to the prevention or treatment of biofilm-associated infections in humans, fitting with the mission of the NIH.